Hello, long time lurker but I just wanted to add to the pattern speculation. I bought a box and my first row was:
Cedric Diggory
Luna Lovegood
Tina Goldstein
Trelawney
Dobby
Dumbledore
Flitwick
Flitwick
Mad Eye Moody
Jacob Kowalski
Jacob Kowalski
Newt
Percival Graves
Harry Potter
Hermione
Ron
Neville Longbottom
Draco Malfoy
Dean Thomas
Cho Chang
The box was sealed when I bought it and it didn't look like anything had moved around. But what I found really interesting was when I got to the second and third row I found the same Harry, Hermione, Ron, Neville, Draco, Dean, Cho pattern repeated. Instead of starting with Graves they both had Credence behind Harry.
I checked this against pictures other people had posted and they seemed to have the same pattern. The only difference is for a lot of people the pattern seems to start further toward the back of the box.
So I was out shopping yesterday morning and noticed a fresh looking box out so decided to have a feel and test my theory. I pulled Ron out first, so I worked back - Hermione, Harry and there he was - Graves. Only difference to my box is he was 3rd from the back, rather than 13th. I then checked the other rows for the trio and worked back to find Credence in both of those.
So my theory is I think the pattern can start anywhere in the row but the figures should be in that order when you find it. Good luck!